1. Field of the Invention
The invention relates to a device for cutting tubes, which rotate around their axis, preferably for severing sections of spiral seam tubes from a run of tubes in production.
2. Description of the Related Art
Spiral seam tubes are produced with spiral seam tube machines from metal strips, which are unwound from coilers, holding metal rolls. In the production of said spiral seam tubes, the metal strip, which can be made, for example, of bright finished steel sheet, galvanized steel sheet, aluminum or inox, is profiled in a roller frame. The profiled metal strip is then laid around a rotating sleeve; and the bead, which is formed by profiling, and the affixed seam merge and are folded over by pressure rollers and completely sealed into a seam. Then the tube, made thus on the sleeve, is slid off the sleeve using push-off rollers. Then with the use of a cutting device of the class, described above, the sections are severed from the tube, which is produced in a well-known spiral seam tube machine and which comprises the helically wound metal strips, whose edges are connected together by means of a seam.
The severed sections of tube are then dumped and carried away.
It is universally known that sections of tubes are severed from a spiral seam tube, which is being produced, with a cutting disk that follows along, but it is also known that the cutting disk cuts poorly. Owing to its high speed, the cutting disk produces such high friction that the tube material heats up to the point that it becomes plastic. The result is lubrication and burrs, which must be removed in a special working step. Furthermore, the heat, generated by the cutting disk, also damages the layer of zinc, a feature that is quite undesirable.
Therefore, the object of the invention is to provide a device of the aforementioned type, with which sections of tube can be severed cleanly from a tube without the formation of burrs. At the same time the severing procedure should not generate any heat that could impair the tube coatings.
The invention solves this problem with a carriage that can be slid back and forth on guides at right angle to the axis of the tube. Said carriage exhibits in the cut plane a milling cutter and shears, both of which can be moved on the tube independently of each other and back again with controlled drives.
In the inventive device the milling cutter makes the notch in the tube""s diameter plane. Then the shears penetrate said notch and execute the round cut, once the milling cutter has been withdrawn.
The milling cutter is preferably a pin-type milling cutter, which can execute in an ideal manner the notch.
The shears are preferably two fork-shaped jaws, which can be positioned at the tube jacket and between which dives a cutting tongue that penetrates the tube jacket. The cutting tongue cuts a strip, equivalent to its width, from the tube jacket. Said strip is wound into a roll during the cutting process; and once the cut is completed, the roll falls off and is fed into a waste basket.
The unit, holding the milling cutter and the shears with their on- and off-devices, is mounted on a carriage, which can be slid parallel to the axis of the tube. This carriage, which is guided at right angle to the moveable carriage, travels along with the tube at its rate of feed so that a clean cut can be executed in the diameter plane.
The unit, holding the milling cutter and the shears with their on- and off-devices, can also be mounted on a carriage, which can be moved at right angle to the axis of the tube and which in turn guided on a carriage, which can be moved parallel to the axis of the tube.
Another embodiment of the invention provides a control, which employs the milling cutter in front of the shears in such a manner that the milling cutter severs the seam and then the control inserts the shears into the cut slot. The shears sever the seam-free peripheral portion of the tube jacket, after the milling cutter has been withdrawn. The seam exhibits four layers of strip material, which the shears normally cannot sever. For this reason the milling cutter, making the notch, is inserted in front of the seam so that the milling cutter severs the seam and the shears have only to cut the unilayered jacket material of the tube.
The control moves the carriage, which can be slid parallel to the tube, at the speed of the tube.
A preferred embodiment provides that the tube stands still while the milling cutter penetrates the tube jacket or rotates only at a decreased rate of production and moves in the axial direction. In this manner good penetration and a good notch are guaranteed. The rate of production is increased again expediently after the milling cutter has penetrated the tube jacket.
In another embodiment of the invention, the rate of production is further increased during the cutting process with the shears, as compared to the rate during the cutting process with the milling cutter. The rate of production during the cutting process with the shears is expediently still below the rate of production between the cutting processes.
Preferably the control of the cutter comprises a computer, for example, an SPS [=series parallel series] control. An especially preferred embodiment provides that the control controls the use of the milling cutter and the shears and the speed of the carriage, carrying the milling cutter and the shears, as a function of the speed of the metal strip, flowing into the spiral seam tube machine. The number of revolutions of the tube and the speed of the tube in the axial direction can be computed from the metal strip""s rate of feed so that these values, computed by the computer, can be used to control the milling cutter and the shears, as well as the carriage, carrying them.